The Impact of Olfactory Stimulation on Dreams

ProblemOnly a limited number of trials is available regarding the impact of external and internal stimuli on human dreams. Current research focuses on the question whether these stimuli (acoustic or mildly painful stimuli e.g.) are incorporated into dreams and whether they influence their emotional coloring. In a recently published trial we were able to demonstrate that isolated olfactory stimulation does not lead to arousals. Aim of the present study was to investigate whether olfactory stimuli of different hedonic characteristics influence dreams in humans.Methods15 young healthy female volunteers were investigated during 30 nights of testing. Standardized awakenings were performed during REM sleep. During REM phases, subjects were exposed to non‐odorous control, a positive odor (PEA, 20%) and a negative odor (H2S, 4 ppm) for 10 seconds each in a randomized fashion using a computer olfactometer. After the awakening, subjects were advised to report the content of their dream in a standardized fashion and to assess the emotional coloration (positive and negative) on a four digit scale (0/1/2/3: no / little / moderate / strong feelings) to calculate the overall emotional coloration.ResultsIn all subjects, three REM awakenings were performed. For 40 out of 45 awakenings, a dream was reported by the subjects. Mean emotional coloration after control stimulation was slightly positive (+0.5). After negative stimulation, the mean emotional coloration was shifted to negative values (‐0.4) while the mean emotional coloration was significantly more positive after positive stimulation (+1.2).ConclusionStandardized REM awakenings can be performed successfully even under the conditions of an olfactory laboratory with intransal stimulation. With olfactory stimulation, the emotional coloration of dreams can be significantly influenced in accordance with the hedonic aspect of the stimulant.SignificanceThe study opens a potential field of therapeutic intervention with nocturnal olfactory stimulation.